The present invention refers to a bonnet structure for automobiles with improved safety characteristics, in particular in the case of collisions between vehicle and pedestrian due to road accidents.
The bonnet which encloses the motor space of automobiles and other cars is usually realised by means of a bent plate, which defines an outer or upper surface, coupled with a shaped plate, which constitutes the inner or lower surface.
The lower plate is suitably realised so as both to allow the housing inside the motor space of all the apparatuses foreseen for the model of automobile being considered, and to avoid weighing down the entire structure too much, in order to keep good aerodynamic characteristics of the vehicle.
Moreover, conventional bonnet structures to this day constitute a serious source of danger to the safety of pedestrians in the case of collisions in road accidents between vehicles and pedestrians.
Regarding this, the European Community, in accordance with the main automobile manufacturers, has decided to issue a timetable for the introduction of new homogenising laws regarding automobiles, which shall have the purpose of reducing the seriousness of the injuries suffered by pedestrians during road accidents which take place with automobiles.
All of this in order to reduce the substantial cost borne by the Community deriving from the extremely high number of serious injuries to pedestrians, due to the aforementioned road accidents, taking into account the long periods in hospital to give the injured the necessary care.
Although such guidelines are not yet homogenised, a large number of governing institutions, European and private, which have the purpose of checking the xe2x80x9cqualityxe2x80x9d of automobiles as far as the safety of occupants of the vehicle and of third parties is concerned, in the case of road accidents, have already decided to carry out tests regarding this on automobiles currently produced and, moreover, in certain cases to provide public evaluations on the results of such tests.
For example, this is the case of Renault, which, concerning the xe2x80x9cLagunaxe2x80x9d model, has recently advertised recognition received (xe2x80x9cfive starsxe2x80x9d) from a private body concerned with the evaluation of the requirements asked on the subject of passenger safety. The sixth star, which on the other hand concerns passing the passenger collision test, was not obtained.
The tests relative to a collision between automobile and pedestrian involve three different body parts of the pedestrian, and specifically the leg, the thorax and the head. Moreover, for each automobile an area of impact for each of the aforementioned parts of the pedestrian is defined.
In particular, for a collision which involves the area corresponding to the head of the pedestrian (xe2x80x9chead collisionxe2x80x9d) a substantially large area of the bonnet of the automobile is usually involved.
To be specific, xe2x80x9chead collisionxe2x80x9d is defined, according to the current guidelines, as the impact of a mock-up head (consisting of a sphere at least partially made from aluminium and comprising a spherical cover made from rubber which is about 25 mm thick) on the outer surface of the bonnet, according to a predetermined angular direction with respect to the ground.
The guidelines and regulations currently in force determine adaptability criteria, according to which the outer or upper surface of the bonnet of an automobile must be realised in such a way as not to cause serious injury to the pedestrian, in the case of a collision, taking into account determined values of weight, speed and angle of impact of the aforementioned mock-up head on the bonnet. Therefore, for example, the European Authority has issued directives (xe2x80x9cACEAxe2x80x9d phase 1 and xe2x80x9cACEAxe2x80x9d phase 2), based upon which the bonnet structure of an automobile must not cause harm to pedestrians for low weight values of the head, of 3.5 kg and 4 kg, and speed of impact values of 35 km/h and 40 km/h, with an angular direction of collision, with respect to the horizontal direction of the ground, of between 40xc2x0 and 60xc2x0.
In greater detail, the test is conducted by hurling the mock-up head on the outer surface of the bonnet, according to a predetermined angular direction, as stated previously, of between 40xc2x0 and 60xc2x0, with respect to the ground and by detecting the resulting acceleration (acceleration vector rule).
From such an acceleration value a determined function, known as HPC, is then calculated, according to the formula       HPC    =                            (                                    1              /                              (                                                      t                    2                                    -                                      t                    1                                                  )                                      ·                                          ∫                                  t                  1                                                  t                  2                                            ⁢                              a                ⁢                                  ⅆ                  t                                                              )                          2          ,          5                    ·              (                              t            2                    -                      t            1                          )              ,
where |t2xe2x88x92t1|xe2x89xa615 ms, with the acceleration expressed in values referred to as g=9.8 m/s2 and time t in seconds.
From this the function HIC=max (t1xe2x88x92t2) HPC, with |t2xe2x88x92t1|xe2x89xa615 ms is calculated and a maximum HIC value necessary for passing the test is determined.
Currently, the test is considered passed for HIC values of less than 1000, whereas already in the near future such a value could reduce to as low as 800 or 600. From the practical point of view, HIC values equal to such an order of magnitude can be obtained by realising a bonnet, on which the impact of the mock-up head takes place, which is as soft as possible.
However, this implies, apart from constructive problems, that the acceleration during the collision stays within limited values and, consequently, an extremely high deformation of the upper and inner surfaces of the bonnet (or of the protective portion normally present in contact with the outer surface) is obtained.
Moreover, a high deformation or squashing of the bonnet implies the need to foresee a substantial space between the lower surface of the bonnet and the motor housed in the relevant motor space. Such a drawback or the need to add protective material on the outer surface of the bonnet in any case impose stylistic and/or constructive restrictions which are not usually acceptable to automobile manufacturers.
FIG. 1 shows (reference CI) an ideal acceleration curve a (expressed in values of g), as time t varies, worked out mathematically in order to obtain a HIC value lower than the predetermined limit value (1000) and, at the same time, to limit the deformation of the surface of the bonnet (so as to minimise the distance between the aforementioned surface and the motor of the automobile). In reality, the tests conducted on a conventional bonnet show characteristic acceleration curves a (expressed in values of g) according to time t which are substantially discordant with respect to the ideal curve CI.
The same graph of FIG. 1 shows another two curves relative, respectively, to the case of a rigid (unyielding) bonnet, with a HIC value which is thus greater than 1000 (curve PC), and to the opposite case of a substantially yielding bonnet of an automobile (curve SC), the HIC value of which can really be less than 1000. Basically, conventional bonnets in reality have areas of different yield (one thinks, for example, of the more yielding central areas, with respect to the areas at attachments, side supports or hinges, which are more rigid) and this also contributes to increasing the difficulties of realising such structures, taking into account, in the same way, both the regulatory safety requirements and the design requirements.
In such requirements outlined previously, the purpose of the present invention is that of realising a bonnet structure for automobiles with improved safety characteristics, which allows the regulatory requirements concerning collisions with pedestrians and, in particular, those relative to head collisions to be met and, at the same time, which can be realised according to the desired design specifications.
Another purpose of the present invention is that of realising a bonnet structure for automobiles with improved safety characteristics, which allows the prevailing guidelines on the subject to be met uniformly in the various areas of its surface.
A further purpose of the invention is to realise a bonnet structure for automobiles with improved safety characteristics, which allows the guidelines regarding collisions with pedestrians to be met, without for this reason having to foresee great bulks in the bodywork and/or aesthetic profiles of the vehicle which are not pleasing to the eye.
The last but not least purpose of the invention is that of realising a bonnet structure for automobiles which is extremely robust, safe, functional and reliable.
These purposes, according to the present invention, are accomplished by realising a bonnet structure for automobiles with improved safety characteristics, according to claim 1, to which we refer for the sake of brevity.
Advantageously, in order to avoid characteristics of non-uniformity of the upper surface of the bonnet, according to the invention, it is foreseen to place an absorbency system between the upper surface and the lower-surface of the aforementioned bonnet, so that also at the side supports, attachments or hinges of the bonnet (which thus has a rigid underlying portion in those areas) a complete deformation is obtained ensured by the absorbency system. In this way, all of the bonnet structure yields uniformly in order to ensure the necessary safety characteristics in the case of a collision.